1. Field of the Invention
The present invention relates to a spoken dialogue apparatus for performing narrowed retrieval of data desired by a user from a database in accordance with a dialogue.
2. Description of the Related Art
A spoken dialogue apparatus has conventionally used a speech recognition result of a speech input of a user to retrieve data desired by the user from a database. Specifically, the database stores data in association with attribute values concerning a plurality of attributes of the data. The spoken dialogue apparatus presents a response to ask the user to input an attribute value concerning a certain attribute, and retrieves from the database data having, as an attribute value, a speech recognition result of an input speech of the user corresponding to the response.
Japanese Patent No. 3420965 describes a spoken dialogue apparatus which uses a plurality of recognition candidates to retrieve data in the following procedure without narrowing down to one speech recognition result, in order to compensate for inaccuracy of speech recognition. First, a response asking the user to input an attribute value concerning a first attribute is presented, and a first speech recognition result of an input speech of the user corresponding to the response is obtained. Then, a response asking the user to input an attribute value concerning a second attribute is presented, and a second speech recognition result of an input speech of the user corresponding to the response are obtained. In addition, each of the first and second speech recognition results includes a plurality of recognition candidates as described above.
Subsequently, the first speech recognition result and the second speech recognition result are combined to produce a retrieval condition, and desired data is retrieved from the database. That is, such data is retrieved from the database that the attribute value concerning the first attribute is one of the candidates of the first speech recognition result and that the attribute value concerning the second attribute is one of the candidates of the second speech recognition result. The dialogue is ended if the number of data items included in the retrieval result (hereinafter referred to as retrieved data) is less than or equal to a predetermined number, and the retrieved data is presented to the user as the desired data. On the other hand, if the number of retrieved data items is beyond the predetermined number, a response asking the user to input an attribute value concerning another attribute is presented, and combining and retrieval are repeated on the basis of a speech recognition result of an input speech of the user corresponding to the response.
The spoken dialogue apparatus described in Japanese Patent No. 3420965 presents a response asking the user to input an attribute value until the number of retrieved data items becomes less than or equal to the predetermined number. However, a response asking the user to input an attribute value is not necessarily a response that effectively decreases the number of retrieved data items. For example, when the distribution of attribute values concerning attribute which the user is asked to input is not uniform, a significant decrease in the number of retrieved data items cannot be expected. That is, if the recognition candidates included in the speech recognition result of the speech input of the user corresponding to the above-mentioned response are inclined to attribute values having a large number of data items, there is almost no decrease in the retrieved data. Therefore, simply repeating the response asking the user to input an attribute value may unnecessarily increase the number of user inputs and the number of dialogue turns before desired data is presented. The increase in the number of inputs and the number of dialogue turns decreases the degree of satisfaction of the user.
On the other hand, a response asking the user to ascertain whether one of the recognition candidates of the already obtained speech recognition result is a correct attribute value (i.e., the attribute value actually speech input by the user) may be a response that effectively decreases the number of retrieved data items. For example, data which has this attribute value is excluded from the retrieved data if an attribute value having a large number of data items is denied by the user, so that the number of retrieved data items effectively decreases. Alternatively, data which does not have this attribute value is excluded from the retrieved data if an attribute value having a small number of data items is approved by the user, so that the number of retrieved data items effectively decreases.
As described above, the response presented to the user by the conventional spoken dialogue apparatus is not necessarily a response whereby a decrease in the number of retrieved data items can be most expected. Therefore, the number of user inputs and the number of dialogue turns before the spoken dialogue apparatus presents desired data may be unnecessarily increased.